I am looking at buying a pre-owned 1999 Ford Explorer XLT with 4.0 liter V6. I have a '98 and love it, but Old Green is pretty worn out. The '99 was brought inland from southern California. My question is: Are there any horsepower or fuel efficiency differences between those made for the southern California market and elsewhere in the U.S.? Also, are there any changes or adjustments necessary for operating at a higher altitude?

All those altitude changes are made by modern electronics and since you specify Southern CA I say there is no difference in a Southern CA car than a car made for the rest of the state or Nation (in 1999).

My 2004 FORD F-150 has a sticker on it saying “Meets all EPA and CA ULEV standards” one truck that meets all standards,not a seperate vehicle for CA and the rest.

I greatly apreciate your taking time to respond. Just a couple of additional notes: If California emissions are more stringent than the rest of the country, and they are (ppm), then by default, if a car meets California standards, it also meets EPA. Also, at higher altitudes, different fuel octane is needed. At lower levels (like southern California), minimum is 87, however in Colorado, Wyoming, Montana, and other, minimum is 85. Does cause some difference in performance, and can cause “Check Engine” lights to come on (as does oxygenated fuel or fuel that is 10% ethanol. The difference may not be noticeable to most. Just looking for scientific data. Thanks.

The ECM will adjust for altitude up to 10,000 feet. Yes, there WILL be a significant power loss, YOU will lose some power too at high elevation…This has nothing to do with emissions systems or gas octane. It has to do with lack of oxygen…

Ethanol: you’ll get a “too lean” code (P0171?) if you put excessive ethanol in the car. From personal experience, this happens on a '98 Ford Contour at about 40% ethanol.

What happens is that ethanol requires more fuel per qty. of air (a richer mixture) than gasoline. As more ethanol is added, the car automatically adjusts, until its range of adjustment is exceeded, at which point a code is triggered.

I am talking about what type of code you will get if you use correctly blended fuel. You deserve a code if you use a 40% ethanol fuel if your car is not designed for it. The OP was suggesting that 10 ethanol fuels will set codes.

Who was selling 40% ethanol fuel? how did it end up in your car? You can’t blame the manufacture if you use the wrong fuel